In the art of fuel cells, there is that class of fuel cell wherein fuel cell reaction is supported (in part) by a gas, such as the oxygen in air. Such fuel cells typically include metal fuel anode electrodes immersed in electrolytes and flat or partition-like cathode electrodes which include catalytic interface structures of highly active catalytic material with great surface area in contact with the electrolyte and with the gas. While fuel cells of the character referred to above might be theoretically operable and efficient, the establishing of such cells which are effective, dependable and practical has been thwarted by the failure of the prior art to provide gas electrodes which are structurally stable or sound and which are both electrically and chemically effective and efficient.
The effectiveness and efficiency of gas electrodes for fuel cells are primarily dependent upon the provision and use of catalytic barrier structures which are highly active. The activity of such structures is greatly dependent upon the number of active sites and the cumulative surface area presented thereby. Accordingly, such barrier structures are, as a general rule, made up of volumes of finely divided particulate materials such as activated charcoal, which have many active sites and present large surface areas. Since it is necessary that the active sites and/or surfaces of such materials be exposed to and contact the fuel cell electrolytes to effectively support fuel cell reaction, the catalytic barrier structures established thereof must be quite porous and capable of being freely wetted by the electrolytes and permeated by the gases. Accordingly, the active particulate materials making up such catalytic barrier structures cannot be contained and sealed within matrixes of bonding materials or agents, but rather, must be held together and contained by appropriate mechanical means and/or by the use of as little binding material as is possible.
As a result of the foregoing, catalytic barrier structures for gas electrodes for fuel cells are characteristically, if not necessarily, structurally weak and frangible or friable structures which are highly subject to structural failure in the environments in which such electrode structures are used.
In addition to the above, the materials suitable for establishing the catalytic barrier structures for fuel cell gas electrodes and/or the resulting barrier structures are, for the most part, rather poor electric conductors. As a result of the foregoing, such gas electrode structures require and include current collector means to collect current throughout the surface areas of the barrier structures and to conduct that current away for suitable use and to maintain sufficient fuel cell operation.
To the above end, fuel cell gas electrodes provided by the prior art characteristically include woven metal fabric current collectors embodied within the catalytic barrier structures. Such current collectors, in addition to collecting and conducting current away, as required, serve as reinforcing and supporting means for the barrier structures. Though provision and use of such current collector means helps to stabilize the catalytic barrier structures, they are insufficient to establish structurally sound and stable structures suitable for dependable and practical use. Further, while current collectors of metal fabric screen and equivalent metal structures efficiently collect current throughout their related catalytic barrier structures, they have considerable internal resistance and are generally such that they fail to effectively and efficiently conduct the collected current away in an effective manner. Accordingly, they are not very effective and notably limit fuel cell efficiency.
Finally, in fuel cells gas electrodes provided by the prior art, the gas sides or surfaces of the catalytic barrier structures are commonly covered and supported by sheet-like membranes of hydrophobic or water-repellant gas permeable material which establish gas and electrolyte interfaces at the gas sides of the catalytic barrier structures, stop the flow of electrolyte from the catalytic barrier structures, at the gas surfaces thereof, and lend added structural support to said catalytic barrier structures. The sheet materials used to establish such membranes are generally quite thin and fragile and add little overall structural stability to their related catalytic barrier structures. The tendency for such sheet materials to separate or delaminate from their related catalytic barrier structures and to thereby prevent the assembled membranes and barrier structures from operating effectively is so great that the necessary inclusion and use thereof impedes and makes difficult the establishment of structurally sound and practical electrode structures.